1. Field of the Invention
The present invention relates to a magnetic azimuth measurement apparatus which measures a azimuth of earth magnetism.
2. Description of the Related Art
To obtain an azimuth between an external-field such as the earth magnetism and a magnetic sensor device, there is mainly used a conventional method in which directional magnetic sensor devices X161 and Y162 as shown in FIG. 20 are arranged so as to have an orthogonal relationship of 90°, so that two outputs, Xout and Yout, obtained therefrom via a detection/amplifier circuit 163, maybe used as a basis for determining the azimuth
In other words, since outputs of the individual sensors (Xout and Yout) regarding the azimuth θ are expressed by formulas (1) and (2) below because of their directional and positional relationship. the outputs change in sine waveforms with a 90° phase offset (waveforms are shown in FIG. 21).Xout0=cos(θ)  (1)Yout0=sin(θ)  (2)From formulas (1) and (2), a formula (3) is obtained.θ0=Tan−1(Yout0/Xout0)=Tan−1(sin θ/cos θ)  (3)The azimuth θ0 can be calculated from the formula (3).
However, because Tan−1 has discontinuous points, θ0 needs to be corrected according to the following condition:
Condition:If Xout≧0 and Yout≧0, then θ=θ0If Xout<0, then θ=θ0+180°If Xout≧0, Yout<0, then θ=θ0+360°  (4)
An example of the related art is disclosed in Japanese Patent Laid-open Publication 8-201060.
It should be pointed out that it is difficult to obtain the above-mentioned Tan−1 in analog terms (in terms of circuit), hence, it is necessary to carry out calculation by using a microcomputer 164 or the like shown in FIG. 22. Consequently, a system requires an A/D converter 165 which converts an analog output from a sensor to a digital value. Further, because Tan−1 is a nonlinear function, for carrying out its numerical operation, it is necessary to use a large capacity memory 166 such as a numerical table and the microcomputer 164 having a high computational capacity.